That Xid 13 error looks a lot like what I and others have been experiencing for over a year now, with no feedback from nvidia. See for instance these threads:
and there are many, many more threads complaining of what I suspect are the same issue (Xid errors, GPU has fallen off the bus, attempted to release interrupt while in atomic context) causing lockups or crashes. Personally, I am finding the 302 and 304 series drivers to be even more prone to crashing than the 29x series were.
It's rare to see an nvidia dev participate in any of the threads; if they do, they usually just add one comment and then are never seen again. I even emailed their official bug reporting address but I didn't get even get an acknowledgement of receipt.